ActiveRecord::AssociationTypeMismatch Rails 5.0.0.1

[arowan]

My fabricator

Fabricator(:message) do
  user
  subject { Faker::Lorem.sentence }
  body { Faker::Lorem.paragraph }
end

let(:message_attributes) { Fabricate.attributes_for(:message, user: nil) }

I'm setting user to nil and it's throwing this error:

ActiveRecord::AssociationTypeMismatch:
       User(#70254248807040) expected, got String(#70254193623120)

<ActionController::Parameters {"message"=>{"body"=>"Odit consectetur est exercitationem delectus placeat corrupti. Commodi ut et suscipit.", "subject"=>"Porro odio voluptates.", "user"=>""}, "format"=>"json", "controller"=>"internal/messages", "action"=>"create"} permitted: false>

It looks like it's returning user as a blank string. Maybe I'm going about this the wrong way?

[arowan]

The Fabrication gem is working properly and returning a nil value. It's something else, so I've closed this issue.